1. Field of the Invention
The present invention relates to a method for determining the quantity of fuel taken on board an aircraft making it possible to maintain a time requirement of the RTA (the acronym for “Required Time of Arrival”) type. It applies notably to the aviation field and more particularly to flight management devices installed in aircraft.
2. Discussion of the Background
In the general context of air traffic, it is a fact that the density of traffic increases year by year. At the same time, the environmental impact of air traffic must be reduced. Finally, the accident rate must be maintained at the current level or even reduced. Observance of these principles and requirements notably imposes on air traffic control bodies an increasing grip on the flight profiles of the aircraft operating in air space. At the same time, the operators of these aircraft must use devices aimed at satisfying the requests from the air traffic control bodies while minimizing their impact, notably on piloting procedures, the initial flight plan and compliance with the predictions in terms of aircraft operating costs.
Typically, the air traffic control bodies may require aircraft to pass by given points in air space at given times, or RTAs. RTAs allow the air traffic control bodies to ensure a smoothed flow and to manage a stable number of airplanes corresponding to the capacities of the tools at their disposition and to the maximum acceptable load on an air traffic controller. These time constraints are also used to manage the closures and openings of air spaces or of airport installations.
In parallel, it is of great value to the airlines to adjust as well as possible their payloads, and functions for computing the payload have been developed making it possible notably to optimally adjust the fuel payload. Such functions optimize the compromise between the performance of the aircraft, its consumption, and flight safety while holding to the reserves imposed by air traffic regulation.
On board the aircraft, the time requirements of the RTA type, and the payload computations, are usually handled by a flight management system, usually designated by the acronym FMS. An FMS consists of various functional components which allow the aircraft crew to program a flight using a navigation database. The system in this case computes the profiles of lateral and vertical trajectories allowing the aircraft the various Waypoints, often designated by the abbreviation WPT, of the flight plan. These computations are based on the characteristics of the aircraft and on data supplied by the crew, the various onboard sensors and the means of communication with the outside environment. The positioning and guidance functions then collaborate to help the aircraft stay on its trajectory.
There are notably known methods of the prior art, used in FMSs, that make it possible to determine the speed profiles best suited to maintaining a time requirement of the RTA type. Such methods operate on a set of input data comprising a flight plan, a cruising level, the required time constraints and the weight of the aircraft or “airplane weight”. These methods generate as an output a flight criterion or “optimization criterion” making it possible to determine the speed profile of the aircraft. The flight criterion may be a criterion associated with the operating cost of the aircraft, such as the cost index, often designated CI. The CI represents the ratio between the cost of a flight in terms of all the parameters not associated with fuel, including the cost of the flight personnel for example, and its cost in terms of fuel. Other types of flight criteria may be employed, for example criteria associated with flight performance.
There are also known methods of the prior art, often called “Fuel Planning”, that make it possible to make predictions as to the fuel consumed, and therefore to determine the optimal fuel payload. Such methods operate on a set of input data comprising a flight plan, a zero-fuel weight of the aircraft, a cruising level, and an optimization criterion making it possible to determine the speed profile, such as the aforementioned CI. These methods generate as an output a necessary fuel payload and therefore an airplane weight.
This reveals a relationship of partial interdependence between the Fuel Planning methods and the RTA maintenance methods. Therefore, the known methods of Fuel Planning are not compatible with an RTA maintenance method. Consequently, with the current FMSs, when a requirement of the RTA type is defined in a flight plan, a message of the type “Fuel Planning Ignores RTA” is displayed to the pilots of the aircraft.